In recent years, portable storage devices such as a universal serial bus (USB) memory, a Compact Flash memory, or a secure digital (SD) memory card have widely been used. Also, their storage capacities have been increased. These storage devices are able to give and receive an enormous amount of data even if an adequate communication environment is not established between multiple information processing devices. Thus they are highly convenient to use. Further these storage devices include non-volatile memory devices such as flash memories, so they can store data for an extended period of time without requiring a power supply, thereby providing a wide range of applications.
The following references will be described later.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 63-301389    [Patent Document 2] Japanese Unexamined Patent Application    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2002-73422    [Non-Patent Document 1] Japanese News article on Secure USB Memory Service provided by NTT communications, webpage URL “http://enterprise.watch.impress.co.jp/cda/security/2005/03/24/4901.html”, searched on Dec. 20, 2006    [Non-Patent Document 2] Idea CS provided by Mitani corporation, webpage URL “http://tkinfo.mitani-corp.co.jp/product/idea_cs.html”, searched on Dec. 20, 2006